ANCIENT CUESTAS 



837 



the Helderberg escarpment. Westward tlie limestone thickens, and 

 hence the escarpment becomes bold, bnt the inner lowland suffers. 

 In Western Ontario this inner lowland is largely obliterated by 

 drift deposits, but it appears again in the basin of Georgian Bay. 

 The basin of Green Bay likewise occupies a part of the inner low- 

 land in its western extension, south of which the deposits of drift 

 somewhat obscure it. There is, however, a chain of small lakes 

 (Winnebago, etc.) which shows its continuation. Lake Winnipeg 



■'^^v^- 



U AUREAyT-/ 



Fig. 210. A later stage, showing probable river adjustment by capture, etc., 

 as deduced from the present topography. The partial blocking 

 of the valleys by glacial drift, the glacial over-deepening of 

 others, and the subsidence of the land on the northeast, produced 

 the present topography and drainage. 



in Canada lies in a similar inner lowdand faced on the west by a 

 cuesta inface of the Niagaran formation. In a few places the 

 cuesta is broken by ancient or by modern stream channels. The 

 most pronounced of the former is at the western end of Lake 

 Ontario (Dundas Valley) and in the channel connecting Georgian 

 Bay with Lake Huron, and continued in Saginaw Bay (Saginaw 

 River \ alley). (Grabau-i6 : 57-5^.) The most pronounced of the 

 modern stream channels are those of the Genesee and the Niagara. 

 North and west of this cuesta series, i. e., nearer to the old land, 



